Projection exposure apparatus

ABSTRACT

A projection exposure apparatus having a multiple exposure mode includes an illumination system and a projection system. In the multiple exposure mode, a filter which blocks a zero-order light beam among a plurality of light beams coming from a mask illuminated by the illumination system is automatically or manually supplied into an optical path of the projection system. Then, an exposure step in the multiple exposure mode is performed in a state in which the filter has been supplied into the optical path.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an exposure method and anexposure apparatus for exposing photosensitive substrates, such assilicon plate and glass, to light through patterns designed for devices,such as semiconductors including an IC, an LSI, etc., a liquid crystalpanel, a magnetic head, a CCD (image sensor), and so on.

[0003] 2. Description of Related Art

[0004] In manufacturing an IC, an LSI, a liquid crystal element, etc.,by photolithography, a projection exposure apparatus (projectionaligner) is employed. The projection exposure apparatus is arranged toperform an exposure by projecting through a projection optical system apattern of a photomask or a reticle (hereinafter referred to as a“mask”) onto a substrate, such as a silicon plate or a glass plate,which is coated with a photoresist or the liek (hereinafter referred toas a “wafer” in general).

[0005]FIG. 1 schematically illustrates the arrangement of a conventionalprojection exposure apparatus. In FIG. 1, there are illustrated a KrFexcimer laser 191 used as a light source, an illumination optical system192, illumination light 193, a mask 194, exposure light 195 on theobject side, a projection optical system 196, exposure light 197 on theimage side, a photosensitive substrate (wafer) 198, and a substratestage 199 which holds the photosensitive substrate 198.

[0006] In the conventional projection exposure apparatus, a laser beamemitted from the excimer laser 191 is led to the illumination opticalsystem 192. At the illumination optical system 192, the laser beam isconverted into the illumination light 193 having a light intensitydistribution, a luminous distribution, etc., which are predetermined.The illumination light 193 falls on the mask 194. A circuit patternwhich is to be eventually formed on the photosensitive substrate 198 isbeforehand formed on the mask 194 with chromium or the like. Theincident illumination light 193 passes through the mask 194 and isdiffracted by the circuit pattern to become the object-side exposurelight 195. The projection optical system 196 converts the exposure light195 into the image-side exposure light 197 to image the circuit patternon the photosensitive substrate 198 at a predetermined magnificationwith sufficiently small aberrations. As shown in an enlarged view at thelower part of FIG. 1, the image-side exposure light 197 converges on thephotosensitive substrate 198 at a predetermined NA (numericalaperture=sin θ) to form the image there. To have the circuit patternformed in a plurality of shot areas on the photosensitive substrate 198,the substrate stage 199 is arranged to be movable stepwise to vary therelative positions of the photosensitive substrate 198 and theprojection optical system 196.

[0007] However, with the conventional projection exposure apparatususing the KrF excimer laser arranged as described above, it is difficultto form a pattern image of line width not greater than 0.15 μm.

[0008] The reason for this difficulty is as follows. The resolution ofthe projection optical system is limited by a trade-off between anoptical resolution and the depth of focus due to the wavelength of theexposure light. The resolution R of the resolving pattern of theprojection exposure apparatus and the depth of focus DOF can beexpressed by the following Rayleigh's formulas (1) and (2):$\begin{matrix}{R = {{k1}\frac{\lambda}{NA}}} & (1) \\{{DOF} = {{k2}\frac{\lambda}{{NA}^{2}}}} & (2)\end{matrix}$

[0009] In the above formulas, λ represents the wavelength of theexposure light, NA represents a numerical aperture indicative of thebrightness of the optical system on the light exit side, and k1 and k2represent constants which are normally between 0.5 and 0.7.

[0010] According to the formulas (1) and (2), in order to make theresolution R smaller for a higher degree of resolution, it is necessaryeither to make the wavelength λ smaller for a shorter wavelength or tomake the value NA larger for a higher degree of brightness. At the sametime, however, the depth of focus DOF required for a necessaryperformance of the projection optical system must be kept at least at acertain value. This requirement imposes some limitation on the increaseof the brightness value NA.

[0011] There is another known exposure method which does not depend onthe formulas (1) and (2). FIG. 2 is a schematic diagram for explainingsuch an exposure method. Referring to FIG. 2, a coherent light beamemitted from a laser beam source 151 is divided by a half-mirror 152into two light fluxes. Mirrors 153 a and 153 b are arranged to deflectthe two light fluxes respectively at some angles to cause the two lightfluxes to join together on a photosensitive substrate 154 in such a wayas to form interference fringes there. The photosensitive part of thephotosensitive substrate 154 is allowed to sense light according to adistribution of light intensity made by the interference fringes. Then,a periodic protrusion-and-recess pattern is formed according to thedistribution of light intensity by a developing process.

[0012] The resolution R obtained by the above exposure method isexpressed by the following formula (3), wherein the resolution R isassumed to be the width of each of lines and spaces, i.e., the width ofeach of the bright and dark parts of the interference fringes, θrepresents the angle of incidence on the substrate 154 of the two lightfluxes 151 a and 151 b, and NA=sin θ. $\begin{matrix}\begin{matrix}{R = \frac{\lambda}{4\quad \sin \quad \theta}} \\{= \frac{\lambda}{4{NA}}} \\{= {0.25\quad \frac{\lambda}{NA}}}\end{matrix} & (3)\end{matrix}$

[0013] As is understandable by comparing the formulas (3) and (1) witheach other, the constant k1 becomes 0.25 (k1=0.25) according to theexposure method shown in FIG. 2. Considering that the value of theconstant k1 of the conventional projection exposure method is between0.5 and 0.7, the resolution obtainable by the exposure method shown inFIG. 2 is more than two times as high as the resolution obtainable bythe conventional exposure method. According to the exposure method shownin FIG. 2, assuming that X is 0.248 μm and NA is 0.6, for example, theresolution R becomes 0.10 μm.

[0014] However, the exposure method shown in FIG. 2 presents a seriousproblem in that a circuit pattern composed of diverse shapes likesemiconductor element patterns hardly can be obtained by carrying out anexposure according to that method, because only such a line-and-spacepattern that has a uniform pitch over its whole area is obtainableaccording to the method of making an exposure through the interferenceof light fluxes as shown in FIG. 2.

[0015] This problem can be solved, for example, by a known multipleexposure method whereby the projection exposure by the method of FIG. 1and the two-light-flux interference exposure by the method of FIG. 2 arealternately made in combination for one and the same area of aphotosensitive substrate one after another without carrying out anydeveloping process on the substrate at intervals between theseexposures.

[0016] However, the two-light-flux interference exposure in theconventional multiple exposure method necessitates either the use of theapparatus shown in FIG. 2, in addition to the projection exposureapparatus, or the use of a special mask such as a phase-shifting mask inusing the projection exposure apparatus.

BRIEF SUMMARY OF THE INVENTION

[0017] It is an object of the invention to provide a projection exposureapparatus arranged to permit a multiple exposure to be simply carriedout.

[0018] To attain the above object, in accordance with an aspect of theinvention, there is provided a projection exposure apparatus having amultiple exposure mode, which comprises an illumination system and aprojection system, the projection system including means forautomatically or manually supplying into an optical path a filter whichblocks a zero-order light beam among a plurality of light beams comingfrom a mask illuminated by the illumination system, wherein an exposurestep in the multiple exposure mode is performed in a state in which thefilter has been supplied into the optical path.

[0019] In the projection exposure apparatus according to theabove-stated aspect, the filter is arranged to be supplied to a positionof a pupil of the projection system or to a neighborhood of the positionof the pupil. The mask which is used when the filter is supplied to theposition of the pupil of the projection system or to the neighborhood ofthe position of the pupil has a periodic pattern of a pitch which is twotimes a value obtained by dividing a pitch (P) of a periodic patternimage to be formed on an image plane by a projection magnification (M)of the projection system.

[0020] Further, the exposure step in the multiple exposure mode isperformed in such a manner that a first exposure pattern having anexposure amount not exceeding a threshold value of an object to beexposed is formed, an exposure stage different from the exposure step inthe multiple exposure mode is performed in such a manner that a secondexposure pattern having an exposure amount exceeding the threshold valueand an exposure amount not exceeding the threshold value is formed, andthe respective exposure amounts are determined in such a manner that acomposite exposure pattern formed by combining the first and secondexposure patterns is in such a relation to the threshold value that adesired circuit pattern is formed.

[0021] The above and other objects and features of the invention willbecome apparent from the following detailed description of preferredembodiments thereof taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0022]FIG. 1 schematically shows a projection exposure apparatus by wayof example.

[0023]FIG. 2 is a diagram for explaining a two-light-flux interferenceexposure method.

[0024]FIG. 3 is a flow chart showing a flow of an exposure methodaccording to the invention.

[0025] FIGS. 4(A) and 4(B) schematically show exposure patterns obtainedin accordance with the two-light-flux interference exposure method.

[0026] FIGS. 5(A) and 5(B) schematically show exposure sensitivitycharacteristics of resists.

[0027]FIG. 6 schematically shows the formation of a pattern by adeveloping process.

[0028]FIG. 7 schematically shows an exposure pattern obtained by thetwo-light-flux interference exposure.

[0029]FIG. 8 schematically shows a pattern formed in accordance with theinvention.

[0030] FIGS. 9(A) and 9(B) schematically show, by way of example,patterns formed according to a first embodiment of the invention.

[0031] FIGS. 10(A) and 10(B) schematically show other examples ofpatterns formed according to the first embodiment.

[0032] FIGS. 11(A) and 11(B) show still further examples of patternsformed according to the first embodiment.

[0033]FIG. 12 schematically shows a typical circuit pattern.

[0034] FIGS. 13(A) to 13(D) schematically show exposure patterns formedby a two-light-flux interference exposure process according to a secondembodiment of the invention.

[0035]FIG. 14 schematically shows an exposure pattern formed by atwo-light-flux interference exposure process according to a thirdembodiment of the invention.

[0036]FIG. 15 schematically shows a pattern formed by two-dimensionalblocks.

[0037]FIG. 16 schematically shows by way of example a pattern which canbe formed according to the third embodiment.

[0038]FIG. 17 schematically shows a two-light-flux interference exposuremade according to the invention.

[0039]FIG. 18 schematically shows a mask and an illumination methodaccording to the invention.

[0040]FIG. 19 schematically shows essential parts of a projectionexposure apparatus according to the invention.

[0041]FIG. 20 is a flow chart showing a flow of the manufacturingprocess for semiconductor devices according to the invention.

[0042]FIG. 21 is a flow chart showing also a flow of manufacturingprocess for semiconductor devices according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0043] Hereinafter, preferred embodiments of the invention will bedescribed in detail with reference to the drawings.

[0044] One of multiple exposure methods to which the invention isapplied as a first embodiment is first described referring to FIG. 3 toFIGS. 11(A) and 11(B).

[0045]FIG. 3 is a flow chart showing a basic flow of processes of themultiple exposure method. In FIG. 3, there are indicated atwo-light-flux interference exposure step and a projection exposure stepwhich constitute a multiple exposure, in addition to a developing step.The sequence of the two-light-flux interference exposure step and theprojection exposure step does not have to be as shown in the flow chartof FIG. 3. The projection exposure step may be executed before thetwo-light-flux interference exposure step. Further, in a case where eachof the two-light-flux interference exposure step and the projectionexposure step is to be executed a plurality of times, these steps may bealternately executed. Furthermore, some alignment step or the like maybe inserted in between the two-light-flux interference exposure step andthe projection exposure step for the purpose of enhancing image formingprecision. Thus, the structural arrangement according to the inventionis not limited by the flow chart of FIG. 3.

[0046] In the case of the multiple exposure shown in the flow chart ofFIG. 3, a photosensitive substrate is exposed to the light of a periodicpattern composed of interference fringes brought about by theinterference of two light fluxes. FIGS. 4(A) and 4(B) schematically showsuch a periodic pattern. In FIG. 4(A), each numeral indicates the amountof exposure (exposure amount), and the exposure amount of each ofhatched parts is “1” while that of each of white parts is “0”. Indeveloping the photosensitive substrate exposed with the above periodicpattern, an exposure threshold value Eth of the photosensitive substrateis set at a value between “0” and “1”, as shown in FIG. 4(B).

[0047] FIGS. 5(A) and 5(B) show the dependency on the exposure amount Eof the film thickness “d” after developing of a resist part of thephotosensitive substrate and the exposure threshold value Eth for thenegative resist and the positive resist, respectively. The filmthickness “d” after developing becomes “0” at a portion where theexposure has been made to an exposure amount equal to or greater thanthe exposure threshold value Eth in the case of the positive resist, orwhere the exposure has been made to an exposure amount less than theexposure threshold value Eth in the case of the negative resist.

[0048]FIG. 6 schematically shows, for each of the positive resist andthe negative resist, the manner in which a lithography pattern is formedthrough developing and etching processes after the above-statedexposure.

[0049] In the case of the multiple exposure as shown in FIG. 3, if amaximum exposure amount is set to “1” for the two-light-fluxinterference exposure step, the exposure threshold value of the resistis set to a value greater than “1”. In the photosensitive substrate asset in the above manner, in a case where an exposure pattern obtained asshown in FIG. 7 by carrying out only the two-light-flux interferenceexposure is developed, the exposure amount is insufficient, and,although the film thickness somewhat varies, there exists no portionwhere the film thickness becomes “0”, so that any lithography pattern isnot formed (see FIG. 8). The two-light-flux interference exposurepattern then can be considered to have disappeared. (In the following,the use of a negative resist is described by way of example. However,the invention is of course not limited to the use of the negative typenor that of the positive type. Both types of resists are selectivelyusable as desired in accordance with the invention.)

[0050] An advantageous feature of the first embodiment lies in thefollowing point. A high-resolution periodic pattern which seems todisappear if processed by the two-light-flux interference exposure aloneis merged with a pattern obtained by the projection exposure. Then, thehigh-resolution periodic pattern is selectively revived by the abovemerger and reproduced to form a lithography pattern as desired.

[0051]FIG. 9(A) shows a pattern (image) obtained by the projectionexposure step. The resolution in the projection exposure step is abouthalf of that in the two-light-flux interference exposure step.Therefore, in the case of FIG. 9(A), the line width of the pattern(image) formed by the projection exposure step is assumed to be abouttwo times as much as a minimum line width obtained by the two-light-fluxinterference exposure step.

[0052] Assuming that the projection exposure step which gives thepattern of FIG. 9(A) is carried on at the same portion after thetwo-light-flux interference exposure step which gives the pattern ofFIG. 7, without executing the developing step, the distribution of thesum of exposure amounts becomes as shown at the lower part of FIG. 9(B).In this instance, the exposure amount of the two-light-flux interferenceexposure and that of the projection exposure are in the ratio of 1:1.The exposure threshold value Eth is set between exposure amounts “1” and“2” in the same manner as in the case of FIG. 8 showing thedisappearance of pattern. Therefore, when a developing process isperformed after such a double exposure, a lithography pattern is formedas shown at the upper part of FIG. 9(B). This lithography pattern is inrelief (protrusive pattern) in the case of the negative resist and inintaglio (recessed pattern) in the case of the positive resist. Thethus-obtained lithography pattern has the same resolution as in thetwo-light-flux interference exposure, and is not a periodic pattern butan isolated pattern. Thus, this multiple exposure gives a pattern whichis of such a high resolution that is higher than a resolution attainableby the projection exposure and which is not attainable by carrying outthe two-light-flux interference exposure alone.

[0053]FIG. 10(A) shows a case where the projection exposure is carriedout with a pattern of line width twice as large as the above-stated linewidth and at an exposure amount which is greater than the exposurethreshold value Eth (an exposure amount two times as much as theexposure threshold value Eth in this case). After that, when thedeveloping process is carried out, a pattern obtained by thetwo-light-flux interference exposure disappears leaving only alithography pattern formed by the projection exposure, as shown at theupper part of FIG. 10(B).

[0054] FIGS. 11(A) and 11(B) show a case where the projection exposureis carried out with a pattern of line width three times as large as thesmallest line width for the two-light-flux interference exposure. Asshown, the result of this exposure is also the same as in the case ofFIGS. 10(A) and 10(B). As apparent from the above, any projectionexposure with a pattern of a larger line width can be likewise carriedout by basically combining the twofold line width and the threefold linewidth, so that all of the patterns attainable by the projection exposurecan be formed.

[0055] The first embodiment is arranged, as described above, to carryout the two-light-flux interference exposure and the projection exposurein combination. In carrying out the exposures, the exposure amount ofeach exposure is adjusted appositely to the exposure threshold value Ethof the resist of the photosensitive substrate. Any of variouslithography patterns such as those shown in FIGS. 9(B), 10(B) and 11(B)can be formed in such a way as to have its smallest line width becomethe resolution attainable by the two-light-flux interference exposure.

[0056] The above multiple exposure method according to the firstembodiment is recapitulated as follows.

[0057] (i) Any part of the pattern of the two-light-flux interferenceexposure step where the total exposure amount obtained after theprojection exposure step is less than the exposure threshold value iscaused to disappear by the developing process.

[0058] (ii) As regards the pattern areas where the exposure is effectedby the projection exposure step at an exposure amount less than theexposure threshold value, parts of the pattern where the total ofexposure amounts obtained by the projection exposure step and thetwo-light-flux interference exposure step exceeds the exposure thresholdvalue Eth are selectively brought about to have a lithography patternformed by the developing process in such a way as to give the resolutionattainable by the two-light-flux interference exposure.

[0059] (iii) The areas of the pattern at which an exposure is made bythe projection exposure step at an exposure amount greater than theexposure threshold value are included as they are in the lithographypattern formed by the developing process.

[0060] The depth of focus obtained at the two-light-flux interferenceexposure step is fairly large and is, therefore, advantageous in forminga pattern. Further, the sequence of the two-light-flux interferenceexposure and the projection exposure may be conversely arranged.

[0061] The first embodiment of the invention is further described withreference to FIG. 19.

[0062]FIG. 19 schematically shows the exposure method and the exposureapparatus arranged to make an exposure according to the invention. InFIG. 19, reference numeral 11 denotes an exposure light source such as aKrF excimer laser or an ArF excimer laser, or the like. The wavelengthof the exposure light does not exceed 400 nm and is arranged, forexample, to be 248 nm or 193 nm. In FIG. 19, there are furtherillustrated an illumination optical system 12, a schematicrepresentation 13 of illumination modes, a mask 14, a mask 15 which isarranged to be replaced with the mask 14, a mask changer 16, a maskstage 17, a projection optical system 18, pupil filters 19 a and 19 b, afilter changer 20 arranged to have the pupil filters 19 a and 19 beither automatically or manually replaced with each other, a wafer 21,and a wafer stage 22.

[0063] In the exposure apparatus, in a case where the two-light-fluxinterference exposure, which is capable of a projection exposure at ahigh resolution, is to be made, a filter which has a light blocking areaat its center, i.e., the filter 19 a, is used and a coherentillumination which has parallel or approximately parallel light fluxesperpendicularly incident on a mask to make the so-called “σ” small isapplied to the mask which is an ordinary mask having a repeating patternas will be further described later herein.

[0064] Further, in a case where an ordinary projection exposure is to bemade, the illumination is switched over to a partly coherentillumination having a relatively large “σ”, the pupil filter 19 a iseither switched over to the filter 19 b or is retracted without usingthe other filter 19 b, and the mask 14 is replaced with a mask having adifferent pattern.

[0065] In carrying out the two-light-flux interference exposure with theexposure apparatus shown in FIG. 19, the pupil filter 19 a and the mask14 are arranged as follows.

[0066]FIG. 17 shows the projection exposure apparatus having aprojection optical system composed of, for example, a refraction system.In the projection exposure apparatus, a design wavelength is 248 μm andthe numerical aperture NA is not less than 0.6. In FIG. 17, there areillustrated a mask 161, exposure light on the object side 162, theprojection optical system 163, a pupil filter 164, exposure light on theimage side 165, a photosensitive substrate (wafer) 166, and a schematicview 167 showing the position of the light fluxes on the pupil plane, inwhich hatched parts indicate light blocking parts of the pupil filter164. In FIG. 17, the projection exposure apparatus is shown as inprocess of making a two-light-flux interference exposure. As shown inFIG. 17, the object-side exposure light 162 and the image-side exposurelight 165 are composed of three pair of parallel light fluxes and twopair of parallel light fluxes, respectively.

[0067] In order to carry out the two-light-flux interference exposure inan ordinary projection exposure apparatus, the mask and the illuminationon the mask are arranged, according to the invention, as shown in FIG.18.

[0068] Referring to the right part of FIG. 18, the mask 161 has apattern of a one-dimensional period in which light blocking parts 171made of chromium are formed at a pitch Po, which is expressed asfollows: $\begin{matrix}{{Po} = {\frac{2P}{M} = {\frac{4R}{M} = \frac{\lambda}{M \cdot {NA}}}}} & (4)\end{matrix}$

[0069] where R represents the resolution, Po represents the pitch ofarrangement of the light blocking parts 171 on the mask 161, Prepresents the pitch of a periodic pattern image obtained on thephotosensitive substrate 166, M represents the magnification of theprojection optical system 163, λ represents the wavelength, and NArepresents the numerical aperture NA of the projection optical systemobtained on the image side.

[0070] As shown on the left part of FIG. 18, the mask 161 is nearlyperpendicularly illuminated in an almost coherent manner. Under thecoherent illumination, light having passed through the mask 161, whichfalls on the projection optical system 163, includes a zero-order lightflux which rectilinearly travels, a − first-order light flux whichtravels in the direction of an angle −θo and a + first-order light fluxin the direction of an angle +θo. The − first-order light flux and the +first-order light flux travel on the two sides of the zero-order lightflux symmetrically with respect to the optical axis 163 a of theprojection optical system 163. In this case, the pupil filter 164 isretractably arranged in the neighborhood of the pupil (an aperture stop)of the projection optical system 163 to remove the zero-order light fluxso as to prevent the zero-order light flux from contributing to imageformation.

[0071] With the projection exposure apparatus arranged in this manner,the two-light-flux interference exposure step shown in FIG. 3 isexecuted. Then, the multiple exposure can be carried out according tothe invention by using the same projection exposure apparatus. Further,the use of the + and − first-order light fluxes, according to thismethod, permits the mask to be arranged to have a periodic pattern at apitch which is twice as large as the pitch of the conventional maskarrangement. Besides, the multiple exposure method according to theinvention obviates the necessity of attaching a fine phase film to amask like in the case of a Levenson-type mask. The above method is,therefor, advantageous also in respect to the production of masks.

[0072] A second embodiment of the multiple exposure method of theinvention is next described with reference to FIG. 12 and FIGS. 13(A) to13(D). In the case of the second embodiment, a circuit pattern to beobtained by the exposure is a so-called gate-type pattern which is asshown in FIG. 12. In the gate-type pattern, the smallest line width inthe horizontal direction, i.e., in the direction of a line A-A′, is 0.1μm, while the smallest line width in the vertical direction is 0.2 μm.

[0073] In this case, the two-light-flux interference exposure step whichgives a high resolution pattern is applied only to a vertical pattern120, which necessitates the high resolution.

[0074]FIG. 13(A) shows a one-dimensional periodic exposure pattern(distribution of image intensity or exposure amount) obtained by thetwo-light-flux interference exposure. The period of the one-dimensionalperiodic exposure pattern is 0.2 μm, which corresponds to a periodicpattern image of 0.1 μm L&S (line and space). The periodic pattern imageis prepared by using the projection exposure apparatus provided with thezero-order-light-cutting pupil filter shown in FIGS. 17 to 19 and anordinary line-and-space mask pattern. Numerals “0” and “1” shown at thelower part of FIG. 13(A) indicate the amounts of exposure (exposureamounts).

[0075] After the two-light-flux interference exposure step, an exposureis made with an exposure pattern 130 shown in FIG. 13(B) as theprojection exposure. This projection exposure is made also by using theprojection exposure apparatus shown in FIG. 19. The upper part of FIG.13(B) shows a positional relation between the exposure pattern of thetwo-light-flux interference exposure and the exposure pattern of theprojection exposure, and an amount of exposure obtained at each ofdifferent areas by the projection exposure step. At the lower part ofFIG. 13(B), the exposure amounts obtained by the projection exposurestep are shown in a state of being mapped by the resolution of 0.1 μmpitch.

[0076] As is understandable from FIG. 13(B), the smallest line width ofthe exposure pattern of the projection exposure is 0.2 μm, which istwice as large as that of the exposure pattern of the two-light-fluxinterference exposure.

[0077] Further, another method of carrying out the projection exposureto give the exposure pattern wherein the exposure amount varies with thearea of the pattern uses a mask which is arranged as follows. The maskhas a plurality of stepped (multiple) transmission factors includingaperture parts of a transmission factor T% corresponding to the areasindicated by “1” in FIG. 13(B) and aperture parts of a transmissionfactor 2T% corresponding to the areas indicated by “2” in FIG. 13(B). Bythis method, the projection exposure can be finished by carrying it outonly once. In this case, a ratio among the exposure amounts obtained onthe photosensitive substrate by the respective exposure steps is asfollows: “two-light-flux interference exposure”: “projection exposure atthe aperture part of transmission factor T”: “projection exposure at theaperture part of transmission factor 2T”=1:1:2.

[0078] Other types of masks arranged to give exposure patterns in whichthe exposure amount varies with the area of the pattern include a maskwhich has an aperture part analogous to the gate pattern shown in FIG.12. In this case, the image of the vertical pattern 120 which has thesmallest line width cannot be resolved and, therefore, has a smallerexposure amount than other parts. As a result, there is obtained anexposure pattern which resembles the pattern shown at the upper part ofFIG. 13(B).

[0079] Further, there is another method in which an exposure is madetwice by using masks of two kinds which give exposure patterns ofpredetermined exposure amounts as shown at the upper and lower parts ofFIG. 13(D). In the case of this method, since it is sufficient to haveone step of exposure amount, the masks can be arranged in an ordinarymanner to have only one step of transmission factor. The ratio among theexposure amounts obtained on the photosensitive substrate in this caseis as follows: “two-light-flux interference exposure”: “projectionexposure for the first time”:“second projection exposure for the secondtime”=1:1:1.

[0080] The formation of a lithography pattern by the above-statedcombination of the two-light-flux interference exposure and theprojection exposure is next described as follows. In the case of such amultiple exposure, since there is no developing step arranged betweenthe two-light-flux interference exposure and the projection exposure,the exposure amount of the exposure pattern obtained by one exposurestep is added to that of the exposure pattern obtained by the otherexposure step. After the addition, an exposure pattern is newly formedshowing a distribution of exposure amounts and that of latent imageintensity.

[0081] The exposure pattern obtained as a result of the addition of theexposure amounts of the two different exposure steps in the secondembodiment is shown at the upper part of FIG. 13(C). The lower part ofFIG. 13(C) shows, in a gray tone, a lithography pattern obtained bydeveloping the exposure pattern shown at the upper part of FIG. 13(C).Further, in the case of the second embodiment, the exposure thresholdvalue Eth of the photosensitive substrate used is not less than “1” andnot grater than “2”. The lithography pattern is formed in relief(protrusive pattern) in the case of a negative resist and in intaglio(recessed pattern) in the case of a positive resist.

[0082] The lithography pattern shown in gray at the lower part of FIG.13(c) coincides with the gate pattern shown in FIG. 12, so that it isunderstandable that this pattern can be formed by the exposure method ofthe second embodiment.

[0083] A third embodiment of the invention is next described below withreference to FIGS. 14, 15 and 16.

[0084] In the case of the third embodiment, also, the invention isapplied to the projection exposure apparatus having the zero-order-lightcutting pupil filter described with reference to FIGS. 17 to 19, and atwo-dimensional periodic pattern is formed by the two-light-fluxinterference exposure step. FIG. 14 schematically shows atwo-dimensional exposure pattern obtained by the two-light-fluxinterference exposure, as a map of exposure amounts. To increase thepossible variations of the final exposure pattern, the third embodimentis arranged to cause the exposure amounts of the interference fringes(periodic patterns) which are respectively obtained in the two differentdirections (X and Y directions) by the two-light-flux interferenceexposure step to differ from each other. More specifically, the exposureamount in one of the two directions is arranged to be twice as large asthe exposure amount in the other direction. Incidentally, the exposureamounts in the two directions, however, may be arranged to be the sameas each other.

[0085] In the exposure pattern shown in FIG. 14, as a result of thetwo-light-flux interference exposure step, the amounts of exposureobtained on the resist in the two directions X and Y are of four steppedvalues. In order to bring about a sufficient effect over thetwo-light-flux interference exposure, the number of steps of exposureamounts of the projection exposure must be at least five. In addition tothat, the exposure threshold value of the resist applied to thephotosensitive substrate is set at a value greater than “3” which is thelargest exposure amount of the two-light-flux interference exposure andis less than “4” which is the largest exposure amount of the projectionexposure.

[0086] With the projection exposure thus carried out at exposure amountswhich are divided by five steps (“0”, “1”, “2”, “3” and “4”), theexposure amounts of an exposure pattern obtained as a result of theprojection exposure are shown in FIG. 15. In FIG. 15, gray partsrepresent parts having exposure values equal to or above the exposurethreshold value, which parts become an exposure pattern that is finallyconverted by the developing process into a lithography pattern.

[0087] Further, in the case of FIG. 15, the resolution obtained by theprojection exposure step is assumed to be one half of that of thetwo-light-flux interference exposure step, and the exposure pattern ofthe projection exposure is shown in blocks as having a side length twotimes as long as that of the blocks of the two-light-flux interferenceexposure. FIG. 16 shows an example in which an exposure pattern isformed to cover a wider area by varying the exposure amount of theprojection exposure, taking the blocks as the units of variation. In thecase of FIG. 16, the exposure pattern is replete with variations and notonly has the resolution of the two-light-flux interference exposure butalso includes a pattern other than the periodic pattern.

[0088] In the third embodiment, the projection exposure step is executedusing blocks of side length twice as long as that of the two-light-fluxinterference exposure step. However, the invention is of course notlimited to this arrangement. According to the invention, the projectionexposure step can be executed at any desired line width within the limitof resolution of the projection exposure to obtain a correspondingexposure pattern in combination with the two-light-flux interferenceexposure step.

[0089] The line width of the two-light-flux interference exposure in thethird embodiment, as described above, is arranged to be the same in thetwo directions. However, the arrangement may be changed to have the linewidth in one direction different from the line width in the otherdirection. Further, an angle between the two directions, i.e., an angleformed by the two kinds of interference fringes, can be decided asdesired.

[0090] The invention is not limited to the embodiments described above.The sequence of the multiple exposure, the details of the structure ofthe pupil filter, etc., are variable as desired within the spirit andscope of the invention.

[0091] Particularly, the number of times of exposure and the number ofsteps of exposure amounts of the two-light-flux interference exposurestep and the projection exposure step are adjustable and selectable asdesired. Further, the manner in which the exposures are overlapped eachother is adjustable by shifting exposure positions as desired. A circuitpattern thus can be variously formed by such adjustment. Further, theinvention is not limited to the multiple exposure described above. Theinvention is applicable also to various known multiple exposureprocesses which include an exposure step of carrying out atwo-light-flux interference exposure by using a mask and a projectionexposure apparatus.

[0092] Next, a method for manufacturing a semiconductor device with theprojection exposure apparatus arranged according to the invention in themultiple exposure mode described in the foregoing as one of a pluralityof exposure modes is described by way of example below.

[0093]FIG. 20 is a flow chart showing a flow of processes formanufacturing a semiconductor device, such as a semiconductor chip of anIC or an LSI, a liquid crystal panel, a CCD or the like.

[0094] At a step 1 (circuit design), a circuit design for thesemiconductor device is performed. At a step 2 (making of mask), a maskon which the designed circuit pattern is formed is made.

[0095] At a step 3 (manufacture of wafer), a wafer is manufactured byusing a material such as silicon. At a step 4 (wafer process, called apreprocess), an actual circuit is formed on the wafer, by thelithography technique, using the mask and the wafer.

[0096] At a step 5 (assembly, called a postprocess), the wafer obtainedat the step 4 is processed into a semiconductor chip through an assemblyprocess (dicing and bonding), a packaging process (chip sealing), etc.

[0097] At a step 6 (inspection), the semiconductor device obtained atthe step 5 is inspected by carrying out tests for its operation, itsdurability, etc. At a step 7, the semiconductor device thus completedthrough the above tests is shipped.

[0098]FIG. 21 is a flow chart showing the details of the above-statedwafer process. At a step 11 (oxidation), the surface of the wafer isoxidized. At a step 12 (CVD), an insulation film is formed on thesurface of the wafer.

[0099] At a step 13 (formation of electrodes), electrodes are formed onthe wafer by a vapor deposition process. At a step 14 (ionimplantation), ions are implanted into the wafer. At a step 15 (resistprocess), a photosensitive material is coated on the wafer. At a step 16(exposure), the circuit pattern of the mask is applied to the wafer bycarrying out a baking exposure with the projection exposure apparatusdescribed in the foregoing.

[0100] At a step 17 (developing), the exposed wafer is developed. At astep 18 (etching), parts other than the developed resist are scrapedoff. At a step 19 (stripping of resist), the resist which becomesunnecessary after the etching process is removed. With the above stepsrepeated, a multiple circuit pattern is formed on the wafer.

[0101] The manufacturing method described above permits the manufactureof a semiconductor device of a high degree of integration, which hasbeen difficult to attain by the conventional manufacturing method.

1. A projection exposure apparatus having a multiple exposure mode,comprising: an illumination system; and a projection system, saidprojection system including means for supplying into an optical path afilter which blocks a zero-order light beam among a plurality of lightbeams coming from a mask illuminated by said illumination system,wherein an exposure step in the multiple exposure mode is performed in astate in which said filter has been supplied into the optical path.
 2. Aprojection exposure apparatus according to claim 1, wherein said filteris supplied to a position of a pupil of said projection system or to aneighborhood of the position of the pupil.
 3. A projection exposureapparatus according to claim 2, wherein said mask which is used whensaid filter is supplied to the position of the pupil of said projectionsystem or to the neighborhood of the position of the pupil has aperiodic pattern of a pitch which is two times a value obtained bydividing a pitch (P) of a periodic pattern image to be formed on animage plane by a projection magnification (M) of said projection system.4. A projection exposure apparatus according to claim 3, wherein, saidexposure step in the multiple exposure mode is performed in such amanner that a first exposure pattern having an exposure amount notexceeding a threshold value of an object to be exposed is formed, anexposure stage different from said exposure step in the multipleexposure mode is performed in such a manner that a second exposurepattern having an exposure amount exceeding the threshold value and anexposure amount not exceeding the threshold value is formed, and therespective exposure amounts are determined in such a manner that acomposite exposure pattern formed by combining the first and secondexposure patterns is in such a relation to the threshold value that adesired circuit pattern is formed.
 5. A semiconductor-devicemanufacturing method for manufacturing a semiconductor device,comprising a step of printing a device pattern on an object to beexposed, by using a projection exposure apparatus according to one ofclaims 1 to 4.